Security readout for executives and security teams
Plain-English summary
This MongoDB issue can let a low-privileged authenticated user crash replica set secondaries by triggering malformed replication data handling. The business impact is availability: degraded resilience, failover risk, and possible service disruption for databases using affected MongoDB Server versions.
Executive priority
Treat this as a scheduled availability-risk fix unless affected replicated databases support critical services or expose broad low-privilege write access. Prioritize upgrades for internet-adjacent or multi-tenant environments.
Technical view
CVE-2021-20330 is a CWE-20 input validation flaw in MongoDB Server replication handling. An attacker with basic CRUD permissions on a replicated collection could use malformed oplog entries through applyOps, causing denial of service on secondary nodes.
Likely exposure
Exposure is limited to MongoDB Server 4.0 before 4.0.27, 4.2 before 4.2.16, and 4.4 before 4.4.9 in replicated deployments.
Exploitation context
The CVE is not listed as KEV, and the provided sources do not claim active exploitation. Exploitation requires authenticated low-privilege access with CRUD rights on a replicated collection.
Researcher notes
CVSS 6.5 reflects network access, low privileges, no user interaction, and high availability impact only. Sources do not provide public exploit confirmation or detailed workaround guidance beyond fixed version boundaries.
Mitigation direction
- Upgrade affected MongoDB 4.0 systems to 4.0.27 or later.
- Upgrade affected MongoDB 4.2 systems to 4.2.16 or later.
- Upgrade affected MongoDB 4.4 systems to 4.4.9 or later.
- Review CRUD permissions on replicated collections and remove unnecessary access.
- Check MongoDB vendor guidance for any environment-specific remediation notes.
Validation and detection
- Inventory MongoDB Server versions across all replica set members.
- Confirm whether affected deployments use replicated collections.
- Review users and service accounts with CRUD permissions on replicated collections.
- Check monitoring for secondary crashes, restarts, or replication instability.
- Verify upgraded nodes report fixed or later MongoDB versions.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-20: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-20330 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 6.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H2.83.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.5MediumVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://jira.mongodb.org/browse/SERVER-36263CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Input Validation
Improper Input Validation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.